This invention relates to power transmissions and, more particularly, to power transmissions having two input clutches and a plurality of synchronously engaged transmission ratios.
Dual clutch transmission arrangements are generally found with countershaft-type transmissions. That is, these arrangements have a main central shaft and a pair of parallel countershafts and an output shaft. The main central shaft has two clutch arrangements which are operable to selectively interconnect the main power shaft through a head gear set with respective countershafts. The countershafts support a plurality of rotating gear members, which are disposed in continuous mesh with a series of gears and the output shaft.
A ratio interconnection between the countershaft and the output shaft are made by way of a synchronizer or mechanical clutch. The mechanical clutches are arranged such that when the first input clutch is transmitting power, the power path of the second input clutch is free to permit synchronous selection of the on-coming ratio. Then, by swapping the first input clutch for the second input clutch, the power path is changed from the first countershaft to the second countershaft. This permits the stepping of ratios by pre-engaging the nonpower transmitting shaft with the oncoming clutch prior to swapping the input clutches. These types of transmissions have been published in many documents and are well known in the art.
It is also well known that to provide multiple speeds, for example, seven, a dual clutch countershaft-type transmission will require nine and one-half pairs of external gears. This includes two head gear set pairs, one pair each for each forward ratio (other than the direct drive), and one and one-half pairs for a reverse ratio. This transmission will also require four two-way synchronizers.
It is an object of the present invention to provide an improved dual input clutch power transmission incorporating planetary gearsets.
In one aspect of the present invention, a plurality of planetary gearsets are arranged for interconnection with each other.
In another aspect of the present invention, the planetary gear members are interconnectible with the input shaft through a pair of synchronizers, a ground member through a synchronizer, and the output shaft through a synchronizer.
In yet another aspect of the present invention, at least two of the synchronizers are interconnected with respective ones of the input clutches.
In still another aspect of the present invention, three two-way synchronizers and one three-way synchronizer (engages A or B or A and B) are employed to establish in cooperation with the input clutches at least seven forward speed ratios and one reverse speed ratio.
In a further aspect of the present invention, the three-way synchronizer is arranged between two of the planetary members and the output shaft of the transmission.
In a still further aspect of the present invention, two of the synchronizers or mechanical clutches are arranged in series with the input clutches to establish four input power paths to the transmission.
In yet still a further aspect of the present invention, one of the synchronizers is arranged to provide two torque paths between the transmission members and a ground member.
In a yet still further aspect of the present invention, one of the synchronizers is arranged to provide a torque-transmitting connection between two of the planetary members and the output shaft of the transmission.
In another aspect of the present invention, two of the synchronizers are arranged to provide four input nodes to the power transmission, one of the synchronizers is arranged to provide two ground nodes for the power transmission, and one of the synchronizers is arranged to provide two output nodes for the power transmission.
With the present invention, there are seven speed ratios found within the planetary portion of the transmission. There are three underdrive ratios, a direct drive ratio, and three overdrive ratios. The underdrive ratios are all established using the same ground node and the same output node, while the input node is changed. The overdrive ratios are established by using a common ground node and input nodes similar to the underdrive ratios but with a different output node. During the fourth or direct ratio, the synchronizers undergo a plurality of swaps to establish the proper output node for the overdrive ratios.